1. Field of the Invention
The present invention relates to an optical disc apparatus which is used to perform reproducing of information that is recorded on an optical disc or recording of information on an optical disc, especially the present invention relates to technology to prevent collision between a lens and the optical disc.
2. Description of Related Art
Optical disc such as a compact disc (hereinafter referred to as a CD) and a digital versatile disc (hereinafter referred to as a DVD) are widely available from past. Further, optical disc which can record much large capacity of information, such as blu-ray disc (hereinafter referred to as a BD) or the like are developed recently for practical use. For these optical discs, an optical disc apparatus which has an optical pickup is used to perform reproducing of information that is recorded or recording of information.
The optical pickup is made movable along a radial direction of the optical disc and performs reproducing of information which is recorded on the optical disc or recording of information on the optical disc by irradiating light on the optical disc.
In case where reproducing or recording of information is performed utilizing the optical pickup, it is necessary that control is performed such that focus of light which is emitted from a light source is always matched on a recording surface of the optical disc irrespective of waving of surface of the optical disc or the like. (Hereafter, this kind of control is referred to as focus control.) For this purpose, an objective lens which focuses the light emitted from the light source on the recording surface of the optical disc can be moved along a focus direction by an objective lens actuator in the optical pickup. Here, the focus direction is a direction along which the objective lens comes closer to or goes away from the optical disc, and the direction is perpendicular to the recording surface of the optical disc.
In the optical pickup, it is necessary that spot size of light spot which is formed on the optical disc by the light emitted from the light source is made small to be applicable to the optical disc which can record information with high density (for example, BD). As for a method to make the spot size of the light spot small, it is usually performed to make wavelength of the light source from which the light is emitted, shorter and at the same time to make numerical aperture of the objective lens larger.
However, if the numerical aperture of the objective lens is made larger as above described, space between tip of the objective lens and the optical disc (working distance; WD) becomes narrower when reading out or recording on of information for the optical disc is performed by the optical pickup. Here, if explanation about the WD is given more correctly, the WD is distance from the tip of the objective lens to surface of the optical disc when the focus position of the objective lens is matched on the recording surface of the optical disc (See, FIG. 7).
That is, in the optical pickup which requires an objective lens that has large numerical aperture (for example, optical pickup which is formed to perform reading out of information recorded on the BD or recording of information on the BD) the WD becomes very short. Then, if the WD becomes very short, it causes a problem that possibility of collision between the objective lens and the optical disc becomes large. It should be noted that, if the optical pickup formed to perform reading out of information and the like recorded on the DVD or the CD is mounted on an apparatus that requires thinner in size such as note type personal computer and the like, the situation where the WD becomes very short, also happens in the optical pickup. Even in such case, it causes a problem of collision between the objective lens and the optical disc.
Because of these reasons, it is conventionally performed that a protector to prevent collision is made, for example, on the lens holder to hold the objective lens in order to prevent that information recorded on the optical disc may become non readable, or the optical pickup may become non usable due to damage on the objective lens by the collision between the objective lens and the optical disc. (For example, see JP-A-2007-18632, or JP-A-2007-35083.)
However, in case where structure which is shown in JP-A-2007-18632, or JP-A-2007-35083 is employed, the possibility of collision between the protector to prevent the collision and the optical disc remains high still. Then, if the collision of this kind occurs, even though the optical disc is not damaged, there may be a problem that information recorded on the optical disc becomes non readable or the like because ground coom of the protector to prevent the collision which is ground by the collision adheres on the optical disc.
Further, the collision between the objective lens and the optical disc tends to happen when the objective lens is moved along the focus direction to begin the focus control. Further, in an operation to begin the focus control, damage caused by the collision becomes large if the protector to prevent the collision and the optical disc collide with each other when it fails to begin the focus control because the optical disc is in rotating state. Therefore, it is required that this kind of collision is prevented when the focus control is performed.